Thread cut devices for sewing machines, using an upper thread and a lower thread, are used to automatically cut one or both threads. When a cut has been performed during a cut sequence a specific amount of thread has been consumed, since a short piece of thread is normally left under a fabric on which stitches are sewn. Furthermore, a short piece of thread goes through an eye of a needle involved in the stitches, in a known way, and will be consumed when the sewing starts again after a cut sequence. The total thread length used for the sewing of a stitch sequence will therefore be the sum of the thread used for the stitches plus the sum of the thread length that goes out of the eye of the needle at the start of the stitch sequence and the thread length pulled down under the fabric after a cut performed at the end of the stitch sequence.
During specific types of use of a sewing machine, e.g. in embroidery mode, said thread length consumed for the pull down of thread under the fabric can be used when an extra thread consumption is desirable. One example of a situation where an upper thread consumption could be preferable is connected with systems for thread colouring, such as in the sewing machine described in US 20070245940 A1. Said document states that a thread cut may be used to compensate for a possibly incorrect position of a colour change point of the upper thread in relation to a desired colour change of the upper thread as specified according to stitch data. The principle discussed in said document is based on the assumption that a faulty position of the colour change point of the upper thread, after a cut has been performed, is positioned below the fabric. This implies that the position of the thread colour change point is positioned on the piece of thread that has been pulled down under the fabric for carrying out the cut. On conventional sewing machines, provided with a thread cutter controlled by a processor, a typical length of the upper thread pulled out for the cut is around 25 mm (herein referred to as length d). This length d limits the possibilities to adjust a greater error of the position of the colour change point, as well as it limits the possibility for the performance of fine adjustment of the thread length consumed during a cut of the thread.